The mechanism of hepatic uptake or organic anions such as bilirubin is unknown. This lack of information hampers the diagnosis and treatment of hyperbilirubinemia associated with Kernicterus. A previously undescribed serum protein is present in human, rat and rabbit sera which binds these organic anions with high affinity. This suggests that this protein may have an important role in the uptake mechanism. We propose to isolate this protein from human and rat sera and to characterize its physicochemical properties. The interaction of this protein with a variety of organic anions including bilirubin, heme, dyes, bromosulfophthalein, and steroids will be evaluated. This information will be used to aid investigation of the biological function(s) of this protein. Initially, we will examine whether this protein facilitates the uptake of organic anions by isolated rat liver parenchymal cells and eventually by brain cells. Research on this protein is expected to further the understanding of serum transport and hepatic uptake mechanisms and thereby aid the development of improved clinical management of neonatal jaundice.